German Patent Publication DE 41 15 747 C2 discloses a method and an apparatus of the above generally mentioned type. The disclosed apparatus includes a transmitting or emitting part for generating, emitting and deflecting a scanning beam that is to scan the scene of interest, and a receiving part for detecting a reflected beam that arises as a reflection of the scanning beam from objects in the scene. In this context, the emitting part comprises a beam generating source, which emits a laser beam as the scanning beam, as well as two prisms arranged or interposed in the beam path of the scanning beam. One of these two prisms is rotated about a vertical rotation axis and the other prism is rotated about a horizontal rotation axis, so as to deflect and thereby scan the scanning beam in horizontal and vertical directions respectively. Namely, the prism rotating about the vertical axis achieves a horizontal moving deflection or scanning of the scanning beam, while the prism rotating about the horizontal rotation axis achieves a vertical moving deflection or scanning of the scanning beam. Both of these prisms comprise planar parallel side surfaces, on which the scanning beam is refracted. Due to the parallelism of the respective side surfaces, these side surfaces will cause a parallel shifting or translation of the scanning beam by a value that is respectively dependent on the angular position or orientation of the respective prism. Thereby, the prism rotating about the vertical rotation axis causes a horizontal shifting or translation, while the prism rotating about the horizontal rotation axis causes a vertical shifting or translation of the scanning beam. Thereafter, i.e. downstream of the prisms, the scanning beam is directed through a convergent lens and thus projected onto the scene that is to be scanned.
A substantial disadvantage of the known apparatus and method is that two separate prisms are required for achieving the horizontal and vertical deflection or scanning of the scanning beam. These two prisms require a substantial structural space and are each subject to operational interferences or malfunctions. Each prism can also successively add optical distortions or aberrations to the scanning beam.
The Japanese Patent Publication JP 62-008119 A discloses a method and an apparatus including a polygonal mirror having several mirrored side surfaces that are respectively tilted at different angles relative to a rotation axis of the rotating mirror. A scanning beam directed at the rotating polygonal mirror is thus reflected successively from the differently angled mirrored side surfaces, whereby a two-dimensional scanning of a scene by the reflected scanning beam can be achieved. The scanning beam may be a laser beam. This known method and apparatus, however, have the disadvantage, that each one of the mirrored side surfaces of the polygon mirror must be relatively large in order to achieve a deflection of the entire laser beam over the required angular range of the scanning field.
Furthermore, various mirror arrangements having rotatable mirror surfaces arranged at a tilt angle in the beam path of a scanning beam so as to totally reflect the scanning beam and thereby scan a scene with the reflected beam are known in the prior art, for example as disclosed in JP 10-186260 or DE 197 13 826 A1.
It is also known in the prior art to use prism arrangements for scanning a scene, for example as disclosed in EP 0,138,646 A1 or GB 1,562,190, whereby, however, a total reflection of the scanning beam does not arise in any case.